how to notify user of errors in fieldframe extension (EE1)

I’m building a new custom field type for EE 1.6.x using BK/P&T’s FieldFrame API. The custom field type has a fairly involved collection of settings and it’s possible to pick things that will fail. I am using the save_site_settings()/save_field_settings()/save_cell_settings() functions to do the validation on the values the user gives for the various settings, but I haven’t seen a way to give them a “these fields are wrong, go back and try again” message… is this possible? I’d rather present the errors in a more friendly way than just doing something like:

die("you f'ed up some fields")

😉

thanks for any insights.

[Mod Edit: Moved to the Extensions forum]